Clinton campaign debt...Obama's responsibility?

I will not pretend that I am Bill Maher or Chris Matthews but I have followed politics as closely as ever during this presidential race...there is one thing I simply cannot understand. Why is it the nominees responsibility to cover the debt of the loser? This is a question open to all, if someone could explain this to me I would feel much smarter. I have watched the reports, read the articles and I still can't make sense of it. We all watched Hillary go deeper and deeper into debt, going into her personal account to the tune of somewhere around $11 million...all this was done when it was clear that her chances of winning were slimmer than a supermodel. So WHY is it Obama and his campaign financiers duty to clean up her mess? I have nothing against Hillary, she's made history and that is wonderful but it seems to me she was aware of what she was getting herself into. Please post your responses, I beg of you!